The testicle or testis contains several different cell types. These include the germ cells, which make sperm, the supporting and nourishing Sertoli cells, and the hormone-producing interstitial (or Leydig) cells.

This is a common tumor, only found in dogs. It has a patchy worldwide distribution including parts of the Caribbean, USA, Southern Europe, Asia and Africa. It is transmitted by direct physical contact.

Primary Kidney tumors are rare in dogs and cats. When they do occur, they are almost invariably malignant (invasive and spreading) and are called renal carcinoma. These tumors tend to invade the adjacent tissues including the main blood vessel draining the kidney (renal vein).

Most swellings and tumors of the uterus are not cancerous. The most common swelling in the dog is cystic endometrial hyperplasia (overgrowth of the inner lining of the uterus) due to hormone stimulation.

Cancer is a disorder of cell growth (uncontrolled cell division) that results in an abnormal mass of tissue (tumor) without a purpose. The growth exceeds that of normal tissue, is un-coordinated, and persists after the cause has gone. There are many different types of cancers.